In recent years, the talk on Organic Farming is going on. how can we control the weed plants in the field without using the herbicide the question. there are several methods traditionally used and scientifically proved methods are discussed here.

1. Presented by
Nishanth S

2. Weed
Jethro Tull first coined the term ‘weed’ in 1931 in the book “Horse Hoeing
Husbandry”
DEFINITION:
• “Weeds are unwanted and undesirable plant that interfere with utilization of land
and water resources and thus adversely affect crop production and human
welfare.”
• “Weeds are the plants, which grow where they are not wanted.”
(Jethro Tull, 1731)

3. Characteristics of weed
CHARACTERISTICS:
1) In the world 30,000 species of weeds have been listed.
2) Out of which 18,000 cause serious damage to agricultural production.
3) 18 weeds are considered as world worst weeds.
4) These weeds are more competitive than the cultivated crops.
5) They are capable of thriving under stress condition. They produce enormous
seeds.
6) The weed seeds are easily germinated, they undergo pollination very easily.

4. Harmful effects of weeds
Harmful effects of weeds:
• Compete with crop – space, light, moisture, nutrients: YIELD REDUCTION
• Affects quality – farm produce, livestock products such as milk and skin.
• Acts as alternate host – pests and pathogens.
• Causes health problems. Eg., Parthenium causes allergy.
• Increases cost of cultivation – weeding problem.
• Reduces the land value.
• Some weeds are poisonous to livestock.

5. Beneficial effects of weeds
Beneficial effects of weeds:
• As a manure – eg., Calotropis gigantea, Croton sparsiflorus, Tephrosia purpuria
• As human feed – eg., Amaranthus viridis, Digera arvensis as greens
• As fodder – eg., Rynchosia aurea, R. capitata, Clitoria terne (legume fodder)
• As fuel – Prosopis julilora, make charcoal and marketed.
• As soil binder – eg., Panicum repens

6. Beneficial effects of weeds
• As medicine:
• As mats and screens - eg., Cyperus pangorei & C. corymbosus: making mat
Typus angustata: making screen
• As indicators for good and bad soil –
Phyllanthus niruri Jaundice
Eclipta alba Scorpion string
Centella asiatica Improves memory
Cynodon dactylon Asthma, Piles
Cyperus rotundus Stimulated milk secretion
E. colonum Rich soil
Cymbopogon Poor light soil
Sedges Ill-drained soil

7. Classification of weeds
WEED
Life span Ecological
affinity
Soil type Origin Morphology
Annuals
Biennials
Perennials
Wetland
Garden land
Dry land
Black cotton soil
Red soil
Light, sandy or
loamy soil
Lateritic soil
Indigenous
Introduced or
exotic
Grasses
Sedges
Broad leaved
Note : Cyperaceae and typhaceae are not grasses even though they are narrow leaved

11. Yield losses caused by weeds in some plants
• Management of weeds is an important component of production technique as
eliminating of weeds is expensive and hard to achieve.
• The basic approach – to minimize production cost caused by weeds, though
weeds may exist as a part of the whole ecosystem.
CROP
YIELD REDUCTION
(%)
CROP
YIELD REDUCTION
(%)
Rice (transplanted) 30-40 Wheat 20-30
Rice (drilled) 70-80 Soybean 40-60
Maize 50-70 Groundnut 40-50
Sorghum 50-70 Mustard 10-15
Pulses (Kharif) 40-60 Cotton 40-50
Pulses (Rabi) 20-30 Sugarcane 20-30
Potato 30-60
‘Minimum loss in crop production and least disturbance to the ecosystem’

12. About Organic weed management

13. Weed management
• DEFINITION:
“Weed management is the application of certain principles and suitable
methods that will improve the vigour and uniform stand of the crop. At the same
time ignore or discourage the invasion and growth of weeds.”
Evolution of weed management: (6 stages)
1. 10,000 BC Removed by hand
2. 6000 BC Weeds removed by primitive hand tools
3. 1000 BC Weeding done with the help of animal drawn implements
4. 1920 AD Machine drawn implements were used for weeding
5. 1930 AD Weeding was taken up by biological agents
6. 1947 AD Weeding by chemical methods (organic herbicides)

14. Principles of weed management
• Prevention
• Eradication
• Control
• Management
PREVENTION:
1. Use of clean seeds.
2. Avoid the use of raw dung as manure.
3. Avoid movement of livestock and implements from weed infested area to the
clean area.
4. Keep farm fences, roads and bunds clean or free from weeds.
5. Avoid soil transport from weed infested area.
6. Keeping irrigation channels and canal bunds clean.
7. Pull out seedlings in nurseries carefully without weed seedlings.

15. Curative methods
CURATIVE METHODS: control of weeds in the field
A. Eradication methods:
Weeds are destroyed immediately before its multiplication, dispersion and
acclimatization as and when a new weed species is found. It can be done by-
• Destroying the species at the initial stage of introduction and before it produces
any propagule.
• Degenerating the buried dormant viable seeds by fumigation, flooding, heating
and other methods.
B. Control measures:
• In these method weeds are not eradicated but their growth is checked and the
number of weeds is minimized so that they do not affect crop yield.

16. Methods of weed control
METHODS OF WEED CONTROL:
• Mechanical or Physical method
• Cultural mthod
• Chemical method
• Biological method

17. Mechanical method
Hand weeding
 Removal of weeds either manually or by using tools like khurpi or sickle, when
weeds grown upto some extent.
 Effective against annuals and biennials and controls only upper portion of the
perennial.
 Higher labour is required and is tire some.
1. Hand weeding 7. Flooding
2. Hand hoeing 8. Burning
3. Spudding 9. Soil Solarisation
4. Digging 10. Cheeling
5. Sickling 11. Tillage
6. Dredging and chaining 12. Mulching

18. Mechanical method
Hand hoeing
• Hoe has been the most appropriate and widely used weeding tool for centuries.
• Taking out the weeds with the help of khurpi or hand hoes.
• Hoeing by cutting the crown part gives proper control.
• Annuals and biennials can be effectively controlled.
• Convolvulus arvensis which has shallow root system can be controlled.

19. Mechanical method
Spudding
• Hand weeding, hand hoeing added by a sharp edged sickle.
Sickling
• Sickling is also done by hand with the help of sickle to remove the top growth of
weeds to prevent seed production and to starve the underground parts.
• These methods are useful for control of tall growing grasses.
• Especially sickling is useful in irrigation channels, drainage channels and where
undulating topography is present.

20. Mechanical method
Digging
• Digging is useful for patch or spot control of obnoxious / perennial weeds.
• Digging is very useful in the case of perennial weeds to remove the underground
propagating parts of weeds from the deeper layer of the soil.
• They can be eliminated by digging with crowbar or Pick axe etc.
• For large areas, it is not desirable because it is costly and labour oriented.
Mowing
• It is cutting of uniform growth from the entire area up to the ground level.
• It is useful more in non cropped areas than cropped areas. Mowing improves
aesthetic value of an area. Effective against erect and herbaceous weeds.

21. Mechanical method
Cutting
• Cutting is the topping/cutting of the weeds little above ground level.
• It is done with help of axes and saws.
• It is mostly practiced against brushes and trees. In aquatics under water weed
cutters are used.
Dredging
• This is used to control aquatic weeds growing in shallow ditches.
• Mechanical pulling of aquatic weeds along with their roots & rhizomes from the
mud.

22. Mechanical method
Chaining
• Very big & heavy chain is pulled over the bottom of a ditch with tractors along
with embankments of ditch.
• With rubbing action of chain weeds can be fragmented & collected by nets and
hooks.
Burning
• It is cheapest method to eliminate the mature unwanted vegetation in non-cropped
areas and range lands.
• Coagulation of protoplasm occurs with which plant dies.

23. Mechanical method
Flaming
• It is the momentary exposure of green weeds to as high as 1000oC from flame
throwers to control in row weeds.
• Eg. Flaming is used in western countries for selective weed control in crops like
cotton, onion, soybean and fruit orchards. Dodder is also controlled by flaming
in lucern.
Searing
Repeated application of flame to above
ground parts destroyed the root system
and plant dies

24. Mechanical method
Soil Solarization
• It is also called solar soil heating.
• It is effective against weeds which are
produced from seeds.
• It doesn’t involve any tillage of the
field.
• Covering the soil with transparent,
very thin plastic sheets of 20-25mm
polyethylene (PE) film during hottest
part of summer months for 2-4 weeks.
• This increases the temperature by 10-12 0 C over the unfilmed control fields. Then
weeds seeds are desiccated which are present at top 5 cm soil depth.
• Eg: Philaris minor, Avenae and broad leaved weeds controlled by Solarization.
Where as Melilotus sp. posses hard seed coat is resistant to Solarization treatment.

25. Mechanical method
Cheeling
• An implement called cheel (spade
like implement with very long handle)
with which weeds & soil can be
racked up.
• Generally practiced in tea plantations.
Tillage
Most effective and economic method of weed control.
Ploughing, cultivating and harrowing make possible weed control before sowing.
Mould board plough – controls perennial weeds.
Disc harrow and chisel plough Primary tillage operation
Discs, cultivators and harrows Seed bed preparations
Cultivators, discs, rod weeders,
harrow and rotary hoes
Post-seeding weed control

26. Mechanical method
Table: Influence of primary tillage on total weed seeds in soil
Role of tillage in weed control:
a) Facilitating the germination of weed seeds, which can, then, be easily destroyed
by mechanical means.
b) Bringing roots or stolons to the soil surface where they will dry out under the
sunlight.
c) Repeated cultivation, thereby depleting the food reserve of the plant.
d) Uprooting or smothering the weeds with soil.
Soil depth (cm) Total weed seed (%)
Ploughed Chiseled
0-5 20 63
5-10 27 20
10-15 53 17

27. Mechanical method
Puddling:
 Primary objective- to create impervious soil layer to prevent percolation.
 Secondary objective- to destroy weed seeds and weed seed gets decayed.

28. Mechanical method
Intercultivation:
Most effective in the crops sown in rows especially with hoes.
Treatment Weed population
(No./m2)
Weed control
efficiency (%)
Seed yield
(kg/ha)
Unweeded control 216.93 - 783.19
One hoeing (25 DAS) 100.45 39.72 897.38
Two hoeing (25 & 50 DAS) 18.85 92.32 245.72
Table: Effect of hoeing on weed population, weed control efficiency and yield of greengram
(Panwar etal., 1999)

29. Mechanical method
Mulching
• Principle is exclusion of sunlight from
environment.
• Polythene Sheets, natural materials
like paddy husk, ground nut shells,
saw dust etc. are used as mulching
material.
• The thickness should be enough to cut
off light (i.e. 10-15 cm)
• The efficiency of polythene sheet is more (more polythene) if it is applied in
continuous sheet rather than in particle farm.
• It is effective against annual weeds and perennial weeds like Cynodon dactylon
and Sorghum halapense.

30. Mulch
levels
No. of weeds /m2 Weed dry weight (g/m2)
1985-86 1986-87 1985-86 1986-87
No mulch 31.8 16.9 17.4 12.7
Trash mulch 25.9 14.0 15.2 12.1
Table: Effect of mulching on weed growth
(Mann and Chakor, 1993)
Table: Effect of wheat straw mulch on weed growth in maize
Mulch level (t/ha) Weed population
(kg/ha)
Weed dry weight
(kg/ha)
0 220 1500
1.7 160 1800
3.4 67 950
5.1 57 680
6.8 53 570
(Crutchfield, 1986)

31. Mechanical method

32. Cultural methods
Proper crop stand and early seedling vigour
• Lack of adequate plant population is prone to heavy weed infestation, which
becomes, difficult to control later. Therefore practices like
are very important to obtain proper and uniform crop stand capable
of offering competition to the weeds.
1. Proper crop stand and early seedling
vigor
7. Smother crops
2. Selective crop simulation 8. Minimum tillage
3. Proper planting method 9. Summer fallowing
4. Planting time 10. Lowering area under bunds
5. Crop rotation 11. Flooding and drainage
6. Stale Seedbed
a. Use of high viable seeds c. Adequate seed rate
b. Selection of most adopted crops and crop
varieties

33. Cultural methods
Planting density:
In the crop-weed competitive suituation, by means of narrow spacing or
high seed rate higher number of plants gain bolder canopy cover and thereby
higher weed suppression capacity.
Spacing (cm)
Weed weight
(g/0.25m2)
Grain yield (kg/ha)
20 x 2.5 8.81 4100
20 x 5.0 20.33 3700
20 x 10.0 13.87 3000
20 x 15.0 23.09 3200
20 x 20.0 26.16 3900
Table: Effect of spacing on weed growth in transplanted paddy
(Kim and Moody, 1981)
Decreaseinspacing
Increaseinyield

34. Cultural methods
Planting direction:
• Crops sown in North-South direction suppress weed growth better than East-West
direction.
• East-West crop allows sunlight to reach weeds throughout the day whereas,,
North-South sown crop utilizes more light, shades weeds and does not allow light
to reach weeds.
Seed rate (kg/ha) Grain yield
(kg/ha)
Dry matter of
weeds (kg/ha)
100 3477 831
125 3549 457
150 3688 280
Table: Effect of seed rate on weed dry matter and yield of wheat
(Bhan, 1987)

35. Cultural methods
Selective crop simulation:
• Selective simulation can be achieved by
a) application of soil amendments like gypsum or lime may correct the soil
conditions in favour of crop growth
b) addition of FYM or synthetic soil conditioners to very light or heavy soils
may improve the soil structure and maintaining better air water relationships and
ultimately it improving the crop growth
c) manures and fertilizers application of proper kind in adequate quantities
improve the crop growth.
d) Inoculation of crop seeds with suitable nitrogen fixing and phosphorous
solubilising organisms may helps in selective simulation of some crops.
Eg: Legume crop and non legume weed. Selective simulation in wide row crops like
maize, sugarcane, cotton can be achieved by foliar application of nutrients.

36. Cultural methods
Proper planting method
• Any planting method that leaves the soil surface rough and dry will discourage
early growth.
• Plough planting (minimum tillage) methods proved to be very useful to reduce
early weed growth.
• In summer, furrow planting of crops reduce the weed problems. Because in this
method irrigation water restricted initially to the furrow only.

37. Cultural methods
Irrigation methods:
• The weed growth is higher and more pronounced in surface method of irrigation
than drip.
• In Rice, one day after disappearance is always better than continuous
submergence in checking weed growth and improving yield.
• It is more suitable in SRI method of rice planting.
DAT of Cabbage No. of weeds Dry wt. of weeds
Drip Furrow Drip Furrow
30 1409 1844 128 157
60 948 1530 129 170
80 352 1165 44 61
Table: Effect of drip and furrow irrigation on weed intensity in cabbage
(Kudmimani, 1997)

38. Cultural methods
Planting time
• Peak period of germination of seasonal weeds coincides with crop plants.
• So little earlier or later than normal time of sowing is beneficial by reducing early
crop weed competition.
• Eg: Using photo insensitive varieties we can make adjustments with regarding to
time of planting.
Treatment Grain yield (kg/ha) Dry matter of weeds @
95DAS (kg/ha)
12 November 4148 1662
24 November 3670 1493
5 December 3637 1124
17 December 2890 9551
Table: Effect of date of sowing on weed dry matter and grain yield of wheat
(Bhan, 1987)

39. Cultural methods
Crop rotation
• Growing of different crops in recurrent succession on the same land is called as
crop rotation.
• Monocropping favors persistence and association of some weeds.
• Crop rotation is effective in controlling of crop associated and crop bound
weeds such as Avena fatua in wheat.
• Wheat-pea and gram break the Avena in wheat, Lucern - grain crop rotation
control Cuscuta.
• The obnoxious weeds like Cyperus rotundus can be controlled effectively by
including low land rice in crop rotation.
Principles in crop rotation:
• Rotation of competitive crops and non-competitive crops.
• Use of weed suppressing crops as cover crops.
• Under sowing cereals with fodder legumes.
• Use of catch crop or trap crop.

40. Cultural methods
Stale Seedbed
• It is the one where one or two flushes of weeds are destroyed before planting of
any crop.
• This is achieved by soaking a well prepared field with either irrigation or rain and
allowing the weeds to germinate.
• These weeds are controlled by using mechanical methods then sow the crop. Here
the advantage is the crop is germinated in weed free environment. In this way,
weed seed bank is exhausted.
Smother crop / Competitive crop
• This crop germinates very quickly and develop large canopy, capable of efficient
photosynthesis within short period.
• They possess both surface and deep roots. Competitive crop smother the ground
quickly than non competitive crop.
• Eg; Cowpea, lucern, berseem, millets.

41. Cultural methods
Growing of intercrops
• Inter cropping suppresses weeds better than sole cropping and thus provides an
opportunity to utilize crops themselves as tools of weed management.
• Many short duration pulses viz., green gram and soybean effectively smother
weeds without causing reduction in the yield of main crop.

42. Cultural methods
Minimum tillage
• Deep and frequent tillage may be useful for some reasons but it serves to bring
more of dominant weed seeds and rhizomes to the soil surface .
• Preserve the new weed seeds deep in the soil for the future Zero tillage
completely avoids burying of weed seeds and reduces persistence of annual
weeds but it induces vigorous growth of perennial weeds.
Treatment Sorghum yield (kg/ha) Weed dry weight (g/m2)
Sorghum + 1 HW 3652 78.7
Sorghum + 2 HW 5264 17.0
Sorghum + Cowpea 1 HW 4895 8.3
Sorghum + Greengram
1HW
3952 14.7
Table: Effect of intercropping on grain yield of sorghum and weed weight at harvest
(Rao and Shetty, 1981)

43. Cultural methods
Summer fallowing
• The practice of summer tillage or off-season tillage is one of the effective
cultural methods to check the growth of perennial weed population in crop
cultivation.
• In the month of April, May and June farmers expose their lands to sun in order to
control many soil born pests, including weeds, roots, rhizomes and tubers of
shallow rooted perennials like Bermuda grass and nut sedge.

44. Cultural methods
Lowering area under bunds
• Bunds are made in field for the purpose of irrigation is ideal places for the rapid
growth of weeds.
• One way of tackle the problem of weeds on bunds is to level the land well so that
less no. of bunds is needed to irrigate the field.
Flooding and drainage
• Flooding is world wide crop husbandry method controlling weeds in rice fields.
• Controls terrestrial weeds: To ensure the effectiveness of flooding the weeds
should be submerged sufficiently for a longer period (i.e. for 2 weeks or more).
Excludes O 2 from environment and kills the weed.
• In M.P. deep flooding of fallow land is followed in rainy season and water is let
out after 2-3 months. This practice locally called Haveli.
• Drainage is used for controlling aquatic and semi aquatic weeds in rice fields,
channels, canals, and ponds.

45. Biological methods
It involves the deliberate use of living organisms like insects, fish, disease
causing organisms or competitive plants to limit weed infestation.
Bioagent:
Ideal characteristics—
 Host specificity
 Ability to kill weed or prevent its reproduction
 Good adaptability
 Reproductive capacity at a rate sufficient to maintain control of host
 High ability to disperse successfully and to locate its host plant.
Strategies
Classical approach Bioherbicide
approach
Naturally occuring
herbicides

46. Classical approach
• Steps involved:
Selection of suitable target
weed species
Selection of suitable bio-
control agents
Introduction, liberation and
establishment of control agents
Selection of survey areas for bio-control agents
Selection of effective bio-control agents
Host specificity determination
1
2
3

47. Classical approach
TYPES OF CLASSICAL BIO-AGENTS
Specific Non - Specific
attack only one or two
specific weeds
Feed upon a variety of
vegetation
Insects
Plant pathogen
Competitive
plants
Carp fish
Snail
Mites

48. SPECIFIC BIO-AGENTS
Insects
Crocidosema lantana (moth) Lantana camara
Plant pathogens
Cephalosporium zonatum Acacia glauca
Puccinia chondrillana Skeleton weed (Chondrilla juncia)
Competitive plants
Marigold & Cassia sericea Parthenium
Panicum purpurascens Typha sp
Carp fish- SPECIFIC
Ctenopharyngodon idella (Chinese grass
carp) Aquatic weeds
Cyprinus carpio (common carp)
Marisa cornuarietis (Snails) roots of water hyacinth, water lettuce and
leaves of “Salvinia”.
Tetranychus desertorum (Mite) prickly pear “Opuntia dellini”

50. Examples of Bio-agents

52. Bioherbicides / Mycoherbicides
“Bioherbicides are pathogens cultured artificially and made available in
sprayable formulations; just like a chemical herbicide.”
Pathogen Weed controlled
Collectotrichum furarioides Asclepias seriaea Common milk weed
Alternaria sp. Crisium avense Canana thistile
Phomomsis convolvulus Convolvulus arvensis Field bind weed
Alternaria crassa Datura stramonium
Bipolaris halepense Sorghum halepense Johnson grass
Collectotrichum oriculare Xanthium spinosum Spiny cocklebur
Alternaria helianthi X. stramarium
Table: Fungi possessing mycoherbicidal activity

53. Bioherbicides / Mycoherbicides
Table: Commercial Mycoherbicides
The rust pathogen, Puccinia abrupta var. parthinicola is capable of
controlling Parthenium hysterophorus.
(Recent report)

54. Characteristics of good mycoherbicides
• They should be
1. Culturable in artificial media
2. Capable of abundant spore production
3. Stable in storage
4. Genetically stable
5. Effective under field conditions
6. Tolerant to variations in temperature
7. Compatible with other chemical/cultural practices
Constraints in bioherbicide approach:
1. Pathogen virulence
2. Environmental reuirements
3. It remains active only on the current weed population

55. Allelopathy in bio-control programmes
1. Use of cover crops for bio-control:
 Parthenium incorporated into soil
reduces growth of Cynodon dactylon.
 Leachets of dry plants of cumin
control weeds.
 Velvet bean suppresses purple nut
sedge.
2. Use of allelochemicals as natural herbicides:
 Xanthotoxin inhibits germination and growth of Lactuca sativa.
 AAL toxin (Alternaria alternate lycopersicii) – effective against dicots at low
concentration.
• The living plant as well as the crop residues with allelopathic potential releases
allelochemicals and suppresses weed growth.

56. Allelopathic potential of some crops
Plant species and common name Inhibition (%)
Medicago sativa (Alfalfa) (cv. Rasen): leaves & stem 100.0
Medicago sativa (Alfalfa) (cv. Yuba) : leaves & stem 100.0
Piper methysticum (Kava): root 100.0
Medicago sativa (Alfalfa) : pellets 85.0
Azadirachia indica Juss neem: leaves & bark 81.3
Leucaena glauca (White lead-tree) 80.7
Ageratum conyzoides (Billy goat weed) 67.0
Galactia pendula (Galactia) 65.4
Eupatorium canabium (Fragrant throughoutwort) 64.9
Oryza sativa (Rice) (cv. Koshihikari): bran 60.7
Melia azedarach (China berry) 58.1
Blechnum orientale (White fern) 52.8

57. References
Websites:
• www.agritechportal.in
• www.angrau.in
Text Books:
• S. C. Panda, Principles and Practices of Organic Farming, pg no. 477- 489
• R. Balasubramanian, K. Balakrishnan, K. Sivasubramaniam, Principles and
Practices of Organic Farming, pg no. 209-219
• S. P. Palaniappan, K. Annadurai, Organic Farming Theory and Practices, pg no.
112-130